Currently, almost 90% of the global water consumption is for irrigation purposes, and more than 40% of the crops are produced under irrigated conditions. In order to assess the future water and food situation, it is therefore necessary to model irrigation water requirements. We present a global model of irrigation requirements, which is based on a new raster map of irrigated areas. With a spatial resolution of 0.5¿, the model simulates the cropping patterns, the growing seasons, and the net and gross irrigation requirements, distinguishing two crops, rice and nonrice. Using long time series of monthly climatic variables, the irrigation requirements under present-day climate conditions are computed, and the impact of climate variability is analyzed. The correspondence between model results and independent estimates of irrigation water use is judged to be good enough for applying the model in global and continental studies.